Method of producing clean walled bores in laminates workpieces

ABSTRACT

A method of enlarging or reaming a bore in a laminated workpiece which consists of selecting a straight fluted reaming tool whose diameter just exceeds that of the bore to be reamed. The reamer is held against rotation while being axially infed into the bore to, concomitantly, kerf the bore wall with its cutting edges. The reamer is then held against further axial movement and rotated to produce a finished bore which does not exhibit that workpiece smear or migration between adjacent laminae which is characteristic of bores formed in a laminated workpiece by infeeding a rotating tool.

United States Patent [191 Cupler, II

[ METHOD OF PRODUCING CLEAN WALLED BORES IN LAMINATES WORKPIECES [76]Inventor: John A. Cupler, II, 10 Cupler Drive, La Vale Cumberland, Md.21502 [22] Filed: 1 Aug. 3, 1971 [21] Appl. No.: 168,649

29/626, 627; 408/22, 30, DIG. 704, DIG. 705, 1; 83/180, 187,185, 52, 54;134/8; 15/104.02, 236, 104.09

[56] References Cited UNITED STATES PATENTS 1,148,065 7/1915 Warren29/557 2,406,938 9/1946 Zehrbach... 408/1 X 3,293,740 12/1966 Enders408/1 X 3,368,257 2/1968 Andreasson 408/705 X 3,370,508 2/1968 Iaia29/558 X 3,457,954 7/1969 Nyberg 29/558 X June 19, 1973 PrimaryExaminer-Charles W. Lanham Assistant Examiner-V. A. DipalmaAtt0rneyColton & Stone [57] I ABSTRACT A method of enlarging or reaminga bore in a laminated workpiece which consists of selecting a straightfluted reaming tool whose diameter just exceeds that of the bore to bereamed. The reamer is held against rotation 'while being axially infedinto the bore to, concomitantly, kerf the bore wall with its cuttingedges. The reamer is then held against further axial movement androtated to produce a finished bore which does not exhibit that workpiecesmear or migration between adjacent laminae which is characteristic ofbores formed in a laminated workpiece by infeeding a rotating tool.

8 Claims, 10 Drawing Figures PATENIEBM $739,461

saw 1 or z FIG. I

(PRIOR ART) FIG. 2

(PRlOR ART) INVENTOR JOHN A. CUPLER, II

Parsmmmw A 3.739.461

SHE 2 of 2 FIG. 6

FIG. IO

FIG. 9

INVENTOR JOHN A. 'CUPLER, II

BY r/ffa ATTORNEY-i METHOD OF PRODUCING CLEAN WALLED BORES IN LAMINATESWORKPIECES BACKGROUND OF THE INVENTION The conventional infeed of arotating cutting tool into a workpiece is inevitably accompanied by asmear or migration of workpiece material along the bore wall. The extentof such workpiece migration may vary from a virtually imperceptible andfunctionally irrelevant smear, occurring as an incident of drillingcertain hard metals having a high melting point, to an obvious migratorysmear in the case of those workpieces characterized by ready cold flow,thermal softening I characteristics and/or low melting points at or neardrilling temperatures. Exemplary of this latter class of materials areplastics, glass and certain metals such as copper. This smear ormigration of workpiece material is, in effect, a displacement orprogression of workpiece material along the bore wall from its originalinsitu position in the direction of tool infeed. The causes are several.In the case of the first mentioned class of materials where migration isminimal, it may involve nothing more than a thin film adherence to thedrill periphery as may be caused by a portion of the removed materialbeing carried and/or comminuted between the drill periphery and the borewall. The advancing drill thus continually migrates material along thebore wall as an incident of the wiping action between the bore wall andthe constantly changing adherent film on the rotating drill.

It is in the formation of bores in the second mentioned class ofmaterials where migration is substantial and which, in many instances,renders the bore so formed unsuitable for its intended purpose that theinvention finds its greatest application. More specifically, theinvention is particularly directed to the formation of clean walledthroughbores in laminated workpieces destined to become circuit boards.

A typical laminated workpiece used in circuit board manufacture maycomprise alternate conductive and non-conductive laminae as exemplifiedby copper and a plastic composite, respectively. Such plastic compositemay comprise, as essential ingredients, epoxy and glass with the formerbeing present in a preponderant proportion. The plastic composite issubject to cold flow which is greatly enhanced by the softening effectcreated by localized heating produced by a drilling operation which mayeven cause actual melting of the plastic material when drilltemperatures run quite high. Under normal drilling conditions, thefrictional heat generated by a rotating drill being infed into alaminated workpiece of the type described will create a condition ofplastic flow in the plastic laminae which clings to the drill as anadherent film until it is at least partially wiped therefrom by contactwith the bore wall as the drill advances. This material which is thusprogressed with the drill in its infeeding direction is that which isreferred to as migrated material. Much of this migrated material from aplastic lamina is deposited on the next adjacent copper lamina while, toa lesser extent, copper is migrated onto a next adjacent plastic lamina.It is the plastic deposit over the copper ring defined by the bore wallthat presents the problem in circuit board manufacture. The purpose informing the throughbores is to provide a conductive path therealongwhich is accomplished by the deposition ofa thin conductive metal filmon the bore wall, such as by electrodeposition. It is apparent thatmetal cannot be electrodeposited on the non-conductive plastic laminaand the continuity of the bore wall deposition depends upon the abilityof the conductive film to deposit on the metal laminae and bridge thenon-conductive gaps represented by the plastic laminae. It is equallyobvious that the presence of migrated plastic over the ring formed ineach individual conductive lamina by the throughbores will defeatroutine efforts to effect a good deposit on the copper rings. Sincethese copper rings must be clean in order to accept the conductiveplating; the usual procedures following the conventional formation of athroughbore and prior to plating the same have involved a separatecleaning operation to remove the migrated metal from the bore wall, orat least from the copper rings. Acid cleaning and vapor blasting are twomethods that have been used. In some cases where material migration isminimal, it has been possible to plate the holes by increasing powerplating factors.

SUMMARY OF THE INVENTION The invention relates to a method ofmechanically removing migrated material from a bore wall. A straightfluted reamer is selected whose diameter just exceeds the bore diameter.The reamer is then inserted, without rotation, into the bore. Theinserting movement is accompanied by a kerfing of the bore wall whichjust exceeds the original bore wall diameter. The reamer is then heldagainst axial movement and rotated to enlarge the bore and remove themigrated material leaving a clean bore wall suitable for plating.

In the process which includes an initial formation of the firstundersize bore by a conventional drilling operation to be followed bythe reaming operation; automatic tool changing equipment which may beused in the practice of the invention is fully illustrated and describedin Applicants U.S. Pat. No. 3,478,419 the disclosure of which patent isherein incorporated by reference.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary section of alaminated workpiece undergoing a conventional drilling operation andwherein the conventional smear or migration of workpiece material isgreatly exaggerated for purposes of illustration;

FIG. 2 is a fragmentary enlargement of the workpiece and drillof FIG. 1;

FIG. 3 is a broken perspective view of a single fluted, gun type reamer;I

FIG. 4 is a broken perspective view of a multiple fluted reamer;

FIG. 5 illustrates the manner of inserting the reamer of FIG. 3 into aconventionally formed bore;

FIG. 6 is a top plan view of FIG. 5;

FIG. 7 illustrates the manner of inserting the reamer of FIG. 4 into aconventionally formed bore;

FIG. 8 is a top plan view of FIG. 7;

FIG. 9 illustrates the reaming of a bore following insertion of thereamer as in FIG. 5; and

FIG. 10 illustrates the clean walled bore resulting from the reamingoperation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A portion of a laminatedworkpiece l0 comprised of tively, is fragmentarily illustrated in FIGS.1 and 2 as having just been conventionally drilled by a helically fluteddrill 16 to form a throughbore 18. The expression plastic, as used inconnection with laminae 14, is used generically to include not onlysynthetic resin compositions but, also, their common filler materialssuch as glass and the like.

The bore wall of throughbore 18 is conventionally smeared with thatplastic material which is progressed or migrated in the direction oftool infeed from its original in-situ position to an adjacent one ormore of the various copper laminae as the rotating drill initiallypenetrates the first plastic lamina. The natural susceptibility of theplastic material to cold flow plus the development of frictionaldrilling heat which causes the plastic to flow more readily in theimmediate vicinity of the tool causes a thin film adherence of theplastic material to the tool which is carried by the tool to the nextadjacent and subsequent copper laminae where a portion thereof is wipedfrom the tool by engagement between the tool and copper laminae. Thethin film adherence of the workpiece material to the tool is indicatedby the reference character 22 while the smear of the same along borewall 20 bears the reference character 24 as is more clearly depicted inthe greatly enlarged showing of FIG. 2. The particular smear of plasticmaterial 24 along the bore wall and particularly across copper laminae22 is greatly exaggerated out of all proportion to the remainder ofFIGS. 1 and 2 solely for the purpose of illustration; it beingunderstood that an accurate scale drawing of FIGS. 1 and 2 would showthe inner surface of the rings formed by the throughbore in each copperlamina to be substantially coincident with the line representation ofthe bore wall 20. It will be appreciated that the migratory effect isprogressive with perhaps a greater proportionate plastic smear at eachcopper lamina deriving from the immediately preceding plastic layer whenconsidered in the direction of tool infeeding movement. This wouldappear to be at least partially explainable on the basis that the copperlaminae are normally harder than the plastic so that there is asubstantially greater wiping effect on the drill as it passes through acopper lamina. workpiece material from the copper laminae is alsomigrated along the bore wall though to a much lesser extent than theplastic and it is the migration of the plastic material that will bemore fully discussed hereinafter with respect to the specific circuitboard workpiece application which has been chosen for purposes ofdescribing the invention.

Upon removal of the tool 16 from bore 18 it is next necessary to cleanbore wall 20 to remove the migrated plastic material smear 24 from theinner peripheral surfaces of the various copper rings created by thedrilling operations so that the same may be plated. This isconventionally done by a separate cleaning operation such as vaporblasting or acid cleaning.

Not only do these prior cleaning operations require a separate set upbut the finished bore wall following such operations lack the precisiondimensions obtainable with a mechanical machining operation.

The method herein described involves a method of mechanically reaming apreviously formed bore to remove migrated material. The reamingoperation may be performed on the same set up used in forming theinitial bore which, advantageously, employs an automatic tool changer ofthe type disclosed in U.S. Pat.

No. 3,478,419. Such a mechanically reamed hole will, of course, producea precisely finished bore.

Essentially, the practice of the invention involves a first step ofinfeeding a rotationally stationary, straight fluted reamer into apreviously drilled hole with only the cutting edges thereof makingsubstantial contact with the bore wall and that contact involving onlysuch penetration of the bore wall as to just exceed the depth ofmigrated material present thereon. The second step involves axiallyrestraining the reamer and rotating the same so that the cutting edgessweep a clean bore wall which bore wall has not been subject to aninfeeding movement to migrate material therealong.

Although it will be apparent that any straight fluted reamer could beused in the practice of the invention, exemplary reamers illustrating,respectively, a reamer requiring a slightly off center infeed withrespect to the initial bore axis and one which is infed coaxial with theinitial bore axis are shown in FIGS. 3 and 4.

The reamer 26 shown in FIG. 3 is, basically, a gun type reamer having asingle flute 28, single semicylindrical land 30, a radiused leading end32 and two straight cutting edges 34. For purposes of the followingdiscussion it will be assumed that the diameter of reamer 26 is equal tothat of the desired finished bore and that the conventional bore 18,formed as described in connection with FIGS. 1 and 2, is just slightlyundersize with respect to the diameter of reamer 26. Reamer 26 is heldagainst rotation and inserted into bore 18 as indicated in FIG. 5. Dueto the fact that reamer 26 has only a single land, the axis 36 thereofis not infed along the original axis 38 of bore 18 but, rather, is justslightly offset therefrom as indicated, in a greatly exaggerated sense,in FIG. 6. The purpose of the slightly offset infeed and the radiusedtool end is to avoid shearing the workpiece material as the reamer isinserted in the bore. Since the diameter of reamer 26 just exceeds thatof bore 18, the insertion of the reamer results in the formation ofkerfs 40 where the cutting edges penetrate the bore wall. It will beunderstood that the depth of each kerf just exceeds the depth of themigrated material 24 and, in a typical circuit board application, may

involve a kerf depth on the order of 0.0002 inch. Al-

though the practice of the invention is independent of the manner inwhich the reamer is inserted, even if it be held by hand for insertionprior to being chucked for rotation; the manner in which the same may beused in a completely automated manner will be apparent from aninspection of U. S. Pat. No. 3,478,419 which, among other things,discloses apparatus for restraining a noncaptive tool against rotationwhile infeeding the same and wherein such tool is resiliently biasedtoward its axis of rotation which readily permits the slight offcenterinfeed above referenced.

Following insertion of the reamer 26 into bore 18 in any desired manner;the reamer is then restrained against axial movement while the same isrotated as indicated in FIG. 9 to produce a clean bore wall such asshown in FIG. 10. The original bore is thus enlarged and the migratedmaterial removed as reamer 26 is rotated. It will be apparent that therotational axis 36 of reamer 26 falls into alignment with the axis 38 ofthe original bore almost immediately upon commencement of rotation asthe broad semi-cylindrical land 30 provides a broad bearing surfacethroughout approximately of the tool periphery. It should be clearlyunderstood that the offset between the initial bore axis and the axis ofthe reamer is described more for enabling one to picture the manner inwhich a single fluted reamer will produce the desired result rather thanas an actual dimensional offset that need be considered as a practicalmatter. Actually, the offset is so infinitesimal it would only berecognized in theory. The purpose of the discussion is, therefore, toexplain how the land 30, whose radius of curvature is just slightlygreater than that of the original bore, can be inserted into the bore.

The explanation will become more clear from an inspection of FIG. 6showing a top plan view of the original bore with the reamer inserted toproduce the opposed kerfs 40 formed by cutting edges 34. As the reamerfirst starts to rotate, the cutting reaction against the leading cuttingedge will cause the tool axis to shift toward the bore axis and the axeswill be coincidently captivated by the engagement of the large land 30with the finished bore wall after the first 180 of tool rotation.Inasmuch as the reamer is not being fed axially, there is no opportunityfor workpiece material to be migrated from one lamina to the next.

The method practiced with a multi-fluted reamer, such as the reamer 42of FIG. 4, is substantially the same as that just described withreference to reamer 26 except that there is no theoretical offset of thereamer and bore axes during insertion. Thus, as shown in FIGS. 7 and 8,reamer 42 is restrained against rotation while the same is inserted intoa bore 18. The cutting edges 44 associated with each of the straightlands 46 thus produce four kerfs 48. Thereafter, reamer 42 is rotated toproduce a clean walled bore.

The gun type reamer 26 is generally preferred in order to reduce theforce required to insert the reamer since it will be apparent that theformation of only two kerfs is less disruptive of the workpiecematerial, thus requiring a lesser infeed pressure then in the case withthe required formation of a greater number of kerfs. Since the finishedbore wall of FIG. 10 exhibits no migrated material across the copperlaminae, the bore wall is in condition to be plated by conventionaltechniques without the requirement for additional preparatory steps.

I claim:

1. a method of reaming a bore in a workpiece to remove migrated materialfrom the bore wall thereof, comprising; selecting a reaming tool havinga diameter just exceeding the diameter of said bore; restraining saidreaming tool against rotation; inserting the rotationally stationaryreaming tool in said bore; and rotating said tool to ream said bore.

2. The method of claim 1 wherein the step of inserting the reaming toolincludes the simultaneous step of kerfing said bore wall.

3. The method of claim 2 including the step of restraining axialmovement of said tool during the rotary reaming operation.

4. The method of claim 3 wherein said workpiece is a laminated workpieceand said bore extends through the laminated workpiece; and wherein thelast named step comprises restraining axial movement of said tool withat least one end of said tool extending beyond one surface of saidworkpiece.

5. The method of claim 4 wherein the step of kerfing said bore wallincludes the step of forming at least two straight, parallel kerfsthroughout the length of said bore.

6. A method of removing migrated material from a substantiallycylindrical throughbore in a laminated workpiece, comprising; selectinga straight fluted reaming tool whose diameter just exceeds that of saidthroughbore; restraining said tool against rotation; infeeding therotationally stationary tool parallel to the axis of said throughborewith the reamer blades of said tool in kerfing engagement with the borewall of said throughbore; terminating the infeed of said tool with saidreamer blades engaging the workpiece throughout the length of saidthroughbore; restraining axial movement of said tool; and rotating saidtool to remove said migrated material.

7. a method of forming a finished bore in a workpiece characterized bythe absence of migrated material throughout the bore wall surfacethereof, comprising; forming a first undersize bore in a workpiece andsimultaneously migrating workpiece material along the bore wall thereof;infeeding a rotationally stationary cutting tool parallel to the axis ofsaid undersize bore and simultaneously forming at least one kerf in theworkpiece intersecting and extending radially outward of said borewalland into said migrated material; terminating the infeed of said toolwith the cutting edge means thereof in engagement with said at least onekerf throughout the total length thereof; and rotating said cutting toolabout said axis to remove said migrated material and enlarge said boreto a finished radius substantially equal to the distance between theradially outermost extent of said kerf and said axis.

8. The method of claim 7 wherein said workpiece is a laminatedworkpiece; and the formation of said at least one kerf comprises theformation of a plurality of straight kerfs.

1. A METHOD OF REAMING A BORE IN A WORKPIECE TO REMOVE MIGRATED MATERIALFROM THE BORE WALL THEREOF, COMPRISING; SELECTING A REAMING TOOL HAVINGA DIAMETER JUST EXCEEDING THE DIAMETER OF SAID BORE; RESTRAINING SAIDREAMING TOOL AGAINST ROTATION; INSERTING THE ROTATIONALLY STATIONARYREAMING TOOL IN SAID BORE; AND ROTATING SAID TOOL TO REAM SAID BORE. 2.The method of claim 1 wherein the step of inserting the reaming toolincludes the simultaneous step of kerfing said bore wall.
 3. The methodof claim 2 including the step of restraining axial movement of said toolduring the rotary reaming operation.
 4. The method of claim 3 whereinsaid workpiece is a laminated workpiece and said bore extends throughthe laminated workpiece; and wherein the last named step comprisesrestraining axial movement of said tool with at least one end of saidtool extending beyond one surface of said workpiece.
 5. The method ofclaim 4 wherein the step of kerfing said bore wall includes the step offorming at least two straight, parallel kerfs throughout the length ofsaid bore.
 6. A method of removing migrated material from asubstantially cylindrical throughbore in a laminated workpiece,comprising; selecting a straight fluted reaming tool whose diameter justexceeds that of said throughbore; restraining said tool againstrotation; infeeding the rotationally stationary tool parallel to theaxis of said throughbore with the reamer blades of said tool in kerfingengagement with the bore wall of said throughbore; terminating theinfeed of said tool with said reamer blades engaging the workpiecethroughout the length of said throughbore; restraining axial movement ofsaid tool; and rotating said tool to remove said migrated material.
 7. amethod of forming a finished bore in a workpiece characterized by theabsence of migrated material throughout the bore wall surface thereof,comprising; forming a first undersize bore in a workpiece andsimultaneously migrating workpiece material along the bore wall thereof;infeeding a rotationally stationary cutting tool parallel to the axis ofsaid undersize bore and simultaneously forming at least one kerf in theworkpiece intersecting and extending radially outward of said bore walland into said migrated material; terminating the infeed of said toolwith the cutting edge means thereof in engagement with said at least onekerf throughout the total length thereof; and rotating said cutting Toolabout said axis to remove said migrated material and enlarge said boreto a finished radius substantially equal to the distance between theradially outermost extent of said kerf and said axis.
 8. The method ofclaim 7 wherein said workpiece is a laminated workpiece; and theformation of said at least one kerf comprises the formation of aplurality of straight kerfs.